Hazardous location heat transfer unit

ABSTRACT

A two chamber heat transfer unit configured such that hazardous air can circulate through one of the chambers and potential ignition source components are contained in another chamber through which the gas to be heated or cooled will circulate.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.14/521,224, filed Oct. 22, 2014, which claims the priority benefit ofU.S. Provisional Patent Application No. 61/895,836, filed Oct. 25, 2013,both of which are incorporated herein by reference in their entiretiesas if fully set forth herein.

BACKGROUND

1.Field

This disclosure relates generally to heat transfer units, like airconditioners and heat exchangers, and, more particularly, to heattransfer units used in hazardous environments.

2. Background

In industrial applications, it is not uncommon to have locations wherecooling or heat transfer from a location or housing is needed, yet theambient atmosphere in the area to which the heat will be transferredcontains fine dust or flammable vapor or chemicals which, when subjectedto high heat or localized arcing, become overly corrosive (suchlocations being individually and collectively referred to herein as“hazardous environments”). Such environments can pose a hazard becausemost conventional air conditioning or heat exchanger units containcomponents that have elements which should not be exposed to thehazardous environment, for example, motors, switches and relays, becausethey have the potential to create sparks or have one or moresufficiently hot surfaces that can interact with the dust or vapor tocause an explosion or ignition. Likewise, those sparks and/or hotsurfaces can cause localized atmospheric chemicals to react with andquickly degrade components of the units themselves.

In an effort to address this problem, conventional heat transfer unitsthat are used in such environments typically employ remedial approaches,such as relying upon use of explosion-proof hardware and enclosures,incorporating energy-limiting devices to reduce the possibility ofarcing, or relocating spark-producing or high heat-producing componentsto locations well-removed from the hazardous environment. All suchapproaches however increase cost and complexity of the units.

Thus, there is a need for heat transfer units that can be used inhazardous locations but do not require such high cost and/or complexremedial efforts that have the effect of reducing reliability of theircomponents relative to their normal counterpart components (e.g.,non-explosion proof or energy-limiting).

BRIEF SUMMARY

One aspect involves a heat transfer unit for use in a location whereheat will be transferred by the unit from a heat source in an enclosureto ambient hazardous air. The heat transfer unit has a unitary housingcomprising a first compartment, configured for coupling to and removingheat from the enclosure. The first compartment has therein anevaporator, a motor, and any other potential ignition source within theheat transfer unit. The housing also comprising a second compartment,having an ambient hazardous air inlet, an ambient hazardous air outlet,a condenser and an ambient air movement element located between theambient hazardous air inlet and ambient hazardous air outlet. Theambient air movement element is located such that, during operation ofthe heat transfer unit, the ambient air movement element will move andcause ambient hazardous air to pass into the ambient hazardous airinlet, past coils of the condenser, and out the hazardous ambient airoutlet. The evaporator and condenser are coupled to each other viapiping so as to collectively comprise a cooling circuit for passage of acooling medium therebetween. The motor is coupled to the air movementelement so as to cause the air movement element to move during operationof the heat transfer unit. The first compartment is sealed off from thesecond compartment such that, during operation of the heat transferunit, the first compartment will be sealed off from the hazardousambient air.

Another aspect involves a heat transfer unit for use in a location whereheat will be transferred by the unit from a heat source to ambienthazardous air. The heat transfer unit has a cooling circuit comprisingan evaporator, a condenser, a coolant and passages to contain thecoolant and allow the coolant to circulate between the evaporator andcondenser. The heat transfer unit also has an evaporator compartmentincluding therein the evaporator and ignition source elements of theheat transfer unit, and a condenser compartment including the condensertherein and configured to transfer heat removed from a heat source bythe evaporator to the ambient hazardous air by passing the ambienthazardous air through the condenser compartment. The evaporatorcompartment is sealed off from the condenser compartment such that,during operation of the heat transfer unit, none of the ignition sourceelements of the heat transfer unit will be exposed to the ambienthazardous air.

Yet another aspect involves a method of making a heat transfer unit foruse in a location where hazardous air is present. The method involvesforming a first compartment within a housing including therein allpotential ignition source elements of the heat transfer unit, a firstheat exchange coil, and a first fan configured to cause a gas to enterthe first compartment, interact with the first heat exchange coil, andthen exit the first compartment. The method also involves forming asecond compartment within the housing, sealed off from the firstcompartment, and including therein at least a second heat exchange coil,and a second fan, the second fan being positioned within the secondcompartment so that, when the heat transfer unit is in operation, thesecond fan will cause the hazardous air to enter the second compartment,interact with the second heat exchange coil, and then exit the secondcompartment. The first compartment is configured to be pressurized suchthat, when the heat transfer unit is in operation, the first compartmentwill have a first internal pressure and the second compartment will havea second internal pressure, with the first internal pressure beinghigher than the second internal pressure.

The foregoing and following discussion outlines rather generally thefeatures and technical advantages of one or more embodiments of thisdisclosure in order that the following detailed description may bebetter understood. Additional features and advantages of this disclosurewill be described herein and may be the subject of claims of thisapplication.

BRIEF DESCRIPTION OF THE DRAWINGS

This disclosure is further described in the detailed description thatfollows, with reference to the drawings, in which:

FIG. 1 illustrates, in simplified form, one example implementation of aheat transfer unit in an example hazardous environment;

FIG. 2 illustrates, in simplified form, a side view of the interior ofone example heat transfer unit variant implemented as described herein;

FIGS. 3A-3B respectively illustrate, in simplified form, exampleexterior face panels of the heat transfer unit of FIG. 2;

FIG. 4 illustrates, in simplified form, a side view of the interior ofan example alternative variant heat transfer unit;

FIG. 5 illustrates, in simplified form, a side view of the interior ofanother example alternative variant heat transfer unit;

FIG. 6 illustrates, in simplified form, a side view of the interior ofyet another example alternative variant heat transfer unit;

FIG. 7 illustrates, in simplified form, a side view of the interior of afurther example alternative variant heat transfer unit;

FIG. 8 illustrates, in simplified overview form, a representativeexample of a purge pressurization system connected to heat transfer unitfor use in an environment having ambient hazardous air 104;

FIGS. 9A-9B respectively illustrate, in simplified overview form, anexample of how some variants of the same heat transfer unit as describedherein can, by employing techniques well known in the prior art,function as both a cooling unit and a heat pump;

FIG. 10 illustrates, in simplified form, another example variant heattransfer unit, in this case, in the form of a air-to-air heat exchangerimplementing the principles described herein; and

FIGS. 11A-11B respectively illustrate, in simplified overview form,still other example variant heat transfer units, in this case, in theform of thermo siphon type heat exchangers implementing the principlesdescribed herein.

DETAILED DESCRIPTION

Before describing the details of the devices and approaches herein, itshould be understood that, as used herein, the term “hazardous location”is intended to broadly mean any location (irrespective of geographiclocation) meeting the National Electrical Code definition of a “Class I,Division 1” location where materials in one or more of Groups A, B, Cand/or D are present, and/or meeting the definition of that Codecorresponding to a “Class II, Division 1” location where materials inone or more of Groups D, E and/or F are present.

In addition, as used herein, the term “hazardous air” is intended tomean and encompass air in which flammable gases or vapors may be presentin sufficient quantities to be explosive or ignitable, or air containingcombustible dust or fiber in sufficient quantities so as to be explosiveor ignitable such that the location where the hazardous air is presentwill be a hazardous location as defined herein.

Finally, as used herein, the term “ignition source” is intended tobroadly mean any part or component that gets hot enough to causeignition or explosion of hazardous air, or causes localized arcing orsparks that, when hazardous air is present, can cause ignition orexplosion due to the hazardous air. Examples of heat sources caninclude, but are not limited to, motors, generators, compressors, therotors or brushes of a motor, switches, relays, components that canbuild up a static charge and discharge across a gap (i.e., arc), etc.

With those definitions in mind, some example inventive heat transferunit variants will now be described as representative exampleimplementations employing the invention as claimed.

As a simplified general overview, FIG. 1 illustrates, in simplifiedform, one example implementation of a heat transfer unit, constructedaccording to one of the variants described herein, for coolingelectrical equipment in a cabinet located in an example hazardouslocation.

As shown in FIG. 1, an electrical equipment-containing cabinet 102 to becooled is present in a hazardous environment 104. A heat transfer unit106, constructed and configured as described herein, is connected to theelectrical equipment-containing cabinet 102 to be cooled. In operation,the heat transfer unit 106 will remove heat from the electricalequipment-containing cabinet 102 using a conventional heat transfer orrefrigeration circuit in which a conventional coolant/refrigerantrepeatedly undergoes phase changes as it is circulated between acondenser and evaporator.

With conventional cooling devices for use in a hazardous environment,special explosion-proof components, or components and circuitsdesignated “intrinsically safe” or “electrically safe” to avoid thepossibility of ignition or explosion, must be used. However, inadvantageous contrast to conventional heat transfer unit configurations,the heat transfer unit 106 does not require use of either. This isaccomplished by a construction approach that divides the heat transferunit 106 into at least two chambers 112, 114 that are essentially sealedoff from each other.

In general, the first chamber 112 is exposed to, and circulates, ambienthazardous air 104, to which heat removed from the device to be cooled istransferred. As such, it is constructed to only contain components forwhich there is no risk of a spark or ignition temperatures.

In general, the second chamber 114 is coupled to the cabinet 102 to becooled but is sealed off from the first chamber 112 and the ambienthazardous air 104. The second chamber 114 contains the coolingcomponents as well as any components that could potentially cause aspark or heat to (or above) temperatures that would cause the hazardousambient air to ignite or explode.

Through this two-chamber 112, 114 approach, as will be described ingreater detail below, the ambient hazardous air 104, and the air withinthe cabinet 102 to be cooled, do not generally mix. Advantageously, as aresult, conventional (i.e., those that are not explosion proof, lowpower, “intrinsically safe” or “electrically safe”) components can beused within the second chamber 114, saving cost and complexity.

Specific details and several example alternative implementations of thisapproach will now be discussed.

FIG. 2 illustrates, in simplified form, a side view of the interior ofone example heat transfer unit variant implemented as described herein.As shown in FIG. 2, an electrical equipment-containing cabinet 102 to becooled is present in ambient hazardous air 104. A heat transfer unit 106is coupled to the electrical equipment-containing cabinet 102 to becooled and constructed such that it has at least two chambers 112, 114.The heat transfer unit 106 includes a conventional refrigeration circuitmade up of an evaporator 202, a condenser 204, other components 206,such as, for example, one or more of: a compressor, expansion valve(s),reversing valve(s), sensors, control electronics, electrical heater(s),etc., and piping 208 that allows a heat transfer medium or refrigerantto be circulated therewithin. The heat transfer unit 106 also includes afan 210 that causes the air to be cooled to circulate past the coils ofthe evaporator 202 and, as shown, a blower fan 212 (also interchangeablysometimes referred to as a centrifugal fan or squirrel cage fan) thatcauses ambient hazardous air 104 to circulate past the coils of thecondenser 204 and remove heat emitted therefrom. In addition, the heattransfer unit 106 will also contain other components 214 conventionallycontained in heat transfer units used for the same or similar purposes,components such as, for example, switches, circuit breakers, sensors,electrical or electronic circuitry and wiring to supply power to itsvarious powered parts, as well as control electronics, etc.

In contrast to such conventional units, however, the components of theheat transfer unit of FIG. 2 are advantageously arranged in anunconventional fashion.

Specifically, as shown in FIG. 2, the components are arranged such thatonly the condenser 204 coils and the blades 216 and plenum 218 of theblower 212 are within the chamber 112 through which the hazardous air104 will circulate from the inlet 220, along the path 222 indicated bythe flow arrows through the chamber 112 to the blower 212 where it willbe expelled back out into the ambient hazardous air 104. Thus, onlythese components (and part of the shaft of the blower fan 212 and somepiping associated with the condenser 204) will be exposed to thehazardous air 104. Stated another way, no potential ignition source ispresent in that chamber 112.

Moreover, any piping 208 that passes through the wall 228 between thetwo chambers 112, 114 will be sealed on their exterior to the wall 228,for example, by welding or other appropriate known approach, such thathazardous air 104 cannot pass between the chambers at the wall-pipingjunction.

Likewise, as shown in FIG. 2, the other chamber 114 (through which air,nitrogen or inert gas from the electrical equipment-containing cabinet102 will circulate for cooling) houses all of the other components, suchas for example, the evaporator 202, other components 206, the motor 224of the blower fan 212, and all potential ignition sources. In otherwords, the air or ambient gas (nitrogen or inert gas) from within theelectrical equipment-containing cabinet 102 will be drawn into thatchamber 114 by a fan 210, circulate through the chamber 114 to andthrough the evaporator 202 and then re-enter the electricalequipment-containing cabinet 102 via an outlet 226.

Again, it is worth specifically noting that the two chambers 112, 114are isolated from each other such that essentially none of the hazardousair 104 passing through the chamber 112 will enter the other chamber114. In this regard, it should be noted that the only possible source ofcross flow between the two chambers 112, 114 exists, in the examplevariant of FIG. 2, at the point where shaft of the blower fan 212 passesthrough the wall 228 dividing the two chambers 112, 114. With somevariants, this possibility can be significantly reduced, if noteliminated, by maintaining the chamber 114 at a higher pressure (P+)than the pressure (P) in the chamber 112 through which the hazardous air104 will flow such that, any leakage will be from the chamber 114containing the potential ignition sources 224 to the chamber 112 throughwhich the hazardous air 104 will flow instead of the other way around.In other variants, a sufficiently tight seal about the shaft or, forexample, a labyrinth seal, other tortuous path seal, may be used suchthat any leakage of hazardous air 104 into the chamber 114 that containspotential ignition sources 224 is negligible, if it occurs at all,(i.e., infiltrating hazardous air, if any, will always be sufficientlydilute relative to the overall air, nitrogen or inert gas into which itmay leak so as to present no danger of ignition or explosion).

Returning to FIG. 2, it is worthwhile to point out that the condenser204 is illustrated, in this example, as a two-part condenser so that theentering hazardous air 104 passes through the first and then the secondcondenser before the blower 212 exhausts it back out of the chamber 112.It is to be recognized that the condenser 204 could have alternativelybeen shown as a single condenser or it could have been shown as made upof multiple smaller condensers to increase the surface area for transferof heat. Throughout this document, it should be understood that numerousalternative configurations and layouts of the condenser 204 andevaporator 202, could alternatively be used for purposes of, forexample, conserving space, increasing surface area, to allow forspecific placement of pumps, motors, valves, electronics, etc. withoutdeparting from the principles of the invention which, in the most basicform, places those components that could potentially cause ignition orexplosion of the hazardous air into a chamber that is isolated from thehazardous air and, commonly, but not necessarily, in the path of the airor gas that passes through that chamber (irrespective of whether thatchamber is used to transfer heat away from a heat source (i.e., forcooling) or to a volume (i.e., as a heat pump for heating)), or in anarea where a purge/pressure system can remove, or prevent accumulationof, stagnant or leaked hazardous air within some volume, for example,part of a motor housing or near a corner of a chamber.

FIGS. 3A-3B respectively illustrate, in simplified form, exampleexterior face panels 302, 304 of the heat transfer unit 106 of FIG. 2for both the hazardous air facing chamber 112 (FIG. 3A) and theelectrical component-containing cabinet facing chamber 114 (FIG. 3B).

As can be better seen in the panel 302 of FIG. 3A, the intake 220 forthe hazardous air is sized to provide maximum access to the lower of thetwo parts of the condenser 204 (only a portion of which is visible). Inaddition, from this view, it is more apparent that the blower 212 insidethe chamber 112 is of the type known as a centrifugal blower, which usesa squirrel cage fan 216 to expel the hazardous air from the chamber 112.

In the panel 304 of FIG. 3B, the intake 306, through which air, nitrogenor inert gas will be drawn by the axial fan 210 from the electricalequipment-containing cabinet 102 into the chamber 114, and the outlet226, via which the air, nitrogen or inert gas will be returned to theelectrical equipment-containing cabinet 102, can be better seen.

FIG. 4 illustrates, in simplified form, a side view of the interior ofan example alternative variant heat transfer unit 400 that is similar tothe heat transfer unit 106 of FIG. 2 except that the conventionalcomponents 214 that could potentially be an ignition source, the motor224 for the blower 212 and the motor 402 of the axial fan 210 are allcontained within a sub-chamber 404 of the main chamber 114. In addition,the sub-chamber 404 is configured with an inlet 406 and an outlet 408for a conventional pressure/purge system (not shown in this figure). Inthe unit 400 of this figure, the pressure/purge system uses a compressor(or appropriate pump) to introduce nitrogen, an inert gas or air, underpressure into the sub-chamber 404 via the inlet 406 to thereby maintainthe sub-chamber at a higher pressure (P+) than at least the pressure inthe chamber 112 through which the hazardous air 104 will pass, again sothat leakage of the hazardous air 104 into the vicinity of the blowermotor 224, the fan motor 402 or the conventional components 214 thatcould be an ignition source will be minimized, if not eliminated. Inthis variant implementation, the outlet 408 acts as a check valve toprevent over-pressurizing of the sub-chamber 404.

Thus, it should be appreciated that, with this variant, there is no needto regulate the pressure in the entire chamber 114 relative to thechamber 112 through which the hazardous air will pass, which, dependingupon the size of the unit 400, may be more difficult or expensive toaccomplish. Rather, it is only necessary to maintain the higher pressurein the vicinity of the location where hazardous air might otherwiseinfiltrate, so as to minimize infiltration to below a safe level oreliminate it entirely.

FIG. 5 illustrates, in simplified form, a side view of the interior ofanother example alternative variant heat transfer unit 500 that isalmost identical to the heat transfer unit 400 of FIG. 4 except that,with this variant, only the blower 212 has been replaced by an axial fan506 and only the motor 224 of the axial fan 506 and the motor 402 of thefan for the intake of the chamber 114 containing the potential ignitionsources are contained within a pressurized sub-chamber 504 within thechamber 114.

FIG. 6 illustrates, in simplified form, a side view of the interior ofyet another example alternative variant heat transfer unit 600 that isalmost identical to the heat transfer unit 500 of FIG. 5 except that, inthis variant, only the motor 224 for the axial fan 506 is in thepressurized sub-chamber 604 and the pressurized sub-chamber 604 is notclosed off or otherwise isolated from the chamber 114 within which itresides. Rather, the pressurized sub-chamber 604 includes an opening 602coupling the sub-chamber 604 to the chamber 114. The opening 602 issized to allow the pressure in the sub-chamber 602 to be maintained at apressure (P+) that is higher than the pressure in the chamber 112 forthe hazardous air 104 while allowing for pressure regulation by ventingover pressure from the sub-chamber 602 into the main chamber 114.Depending upon the particular implementation, the opening 602 can simplybe implemented as an appropriate sized hole or it can be implementedusing some form of known check valve or other known vent that can openwhen the pressure exceeds some value and then close when the pressurefalls below that value.

FIG. 7 illustrates, in simplified form, a side view of the interior of afurther example alternative variant heat transfer unit 700 configured asa heat pump to provide heating to a volume 706 sealed off from thehazardous air 104. As shown in FIG .7, the unit 700 uses the sametwo-chamber 112, 114 approach described above, except that the chamber112 exposed to the hazardous air 104 now merely contains an evaporatorcoil 702 and the plenum and fan portion 712 of a blower (and may alsocontain other components that are not potential ignition sources).Likewise, since this configuration is for heating, the other chamber 114contains the condenser coil 704, the other relevant components 206 thatmay be part of the heat pump circuit, the various components 214 thatcould be ignition sources, a fan 708 of a blower and its associatedmotor 710, as well as the motor 714 for the fan 712. Thus, it can beseen that different configurations can be configured with all blowers,all axial fans or some combination thereof as appropriate.

In addition, as with some of the previous variants, this configurationis connected to a purge/pressurization system, only the output nozzle406 of which is shown, to maintain a higher pressure (P+) in the chamberthat contains the potential ignition source(s) 214 than the pressure inthe chamber 112 through which the hazardous air 104 will pass so thathazardous air leakage via the shaft between the motor 714 and the blower712 can be minimized to an acceptable level, if not eliminated entirely.

Moreover, as shown, the wall 228 separates the two chambers 112, 114into unequal sized chambers that are not both purely vertical. It shouldnow likewise be appreciated that that the particular sizing of the twochambers 112, 114 or their orientation, may well depend upon theparticular intended application and available space. For example, insome variants, the heat transfer unit may be configured to mount on topof the cabinet to be cooled or heated, instead of along side of it. Insuch cases, depending upon the particular design, the two chambers 112,114 could be configured with the chamber 112 through which the hazardousair 104 circulates could be on top of the other chamber 114 or alongside it in a more horizontal configuration. Thus, it should beunderstood that the important aspect is having the chamber through whichthe hazardous air will circulate contain none of the components that arepotential ignition sources and a separate other chamber sealed to thevolume to be cooled or heated so that the hazardous air cannot enter thevolume or the other chamber in any concentration near one that thatcould pose a hazard, if it can enter at all.

FIG. 8 illustrates, in simplified overview, a functional representativeexample of a purge pressurization system connected to heat transfer unit800, which may be a cooling unit or heat pump configured with twochambers 112, 114 as described previously, for use in an environmenthaving ambient hazardous air 104. The heat transfer unit 800 is shown assealed to a volume or enclosure 802 (itself sealed off from thehazardous air 104) to or from which it will transfer heat as describedabove. In addition, FIG. 8 illustrates, in simplified overviewfunctional (not physical) form, an example optional purge/pressurizationsystem 804 coupled to (as shown) the volume or enclosure 802 via its owninlet 806, and to the heat transfer unit 800 via an inlet 406 on it asnoted above. The optional purge/pressurization system 804 conventionallycirculates nitrogen, air or an inert gas under pressure and, to do so,includes various components 808, for example, a source of nitrogen, airor inert gas, a pressurization pump, tank, compressor or blower, afilter, and other conventional components typically found in suchsystems. In addition, the purge/pressurization system 804 may furtherinclude auxiliary aspects 810, for example, one or more pressureswitches, a metering valve or a vent. As a further option, for heattransfer units with both a purge/pressurization system inlet 406 andoutlet 408, and/or a closed path purge/pressurization system, thepurge/pressurization system 804 may additionally include a return path812 that allows the nitrogen, air or inert gas to return to thepressurization pump or blower component(s) 808. For non-closed pathconfiguration systems (i.e., where the nitrogen, air or inert gas doesnot return, but rather is vented, the illustrated return path 812 maysimply be a control feedback path (electrical or mechanical).

At this point, it should be noted that the purge/pressurization systemis an optional adjunct to the heat transfer units as described herein.In other words, such a system could already be part of the volume orenclosure 802 to be heated or cooled and tapped into for use with a heattransfer unit or it could be provided as part of the heat transfer unit,or some combination thereof, or it could be dispensed with entirely ifthe nitrogen, air or inert gas in the volume or enclosure 802 to beheated or cooled can be introduced into the chamber 114 at a sufficientpressure to maintain the chamber at a sufficiently higher pressure (P+)than the pressure in the other chamber 112 through which the hazardousair 104 will pass.

Finally, FIGS. 9A-9B respectively illustrate, in simplified overviewform, an example of how some variants of the heat transfer unitsdescribed herein can, by employing techniques well known in the priorart, function as both a cooling unit and a heat pump to, respectively,either cool or heat a spatial volume or enclosure 900.

Specifically, as shown in FIG. 9A, the spatial volume or enclosure 900is to be cooled. As such, the coil 902 within that spatial volume orenclosure 900 will act as an evaporator coil such that, when a fan 904 acauses the ambient gas in the spatial volume or enclosure 900 to passover the coil 902, heat will be removed from the ambient gas. This isaccomplished, in a conventional manner, by continuously circulating arefrigerant (directionally indicated by the arrows) from a compressor906 to a coil 908 that acts as a condenser (over which a fan 904 b willpass the ambient gas to remove heat from the coil 908), through anexpansion/metering valve 910 to the coil 902 that acts as theevaporator.

Advantageously, through inclusion of a reversing valve 912 in thecircuit, by changing the setting of the reversing valve 912, thedirection of the refrigerant flow can be reversed through the coils,902, 908 such that, as shown in FIG. 9B, the coil 902 in the spatialvolume or enclosure 900 will now act as the condenser and the other coil908 will now act as the evaporator.

In this manner, the same configuration of some heating unitimplementation variants as described herein can be configured to eitherheat or cool merely by including a reversing valve in the refrigerationcircuit and setting it accordingly.

Up to now, the heat transfer units discussed have been air conditioner(i.e., cooling) units or heat pumps. However, the foregoing is notlimited to those types of devices, but rather should also be understoodto encompass heat exchanger units as well.

In that regard, FIG. 10 illustrates, in simplified form, another examplevariant heat transfer unit 1000, in this case, in the form of aair-to-air heat exchanger implementing the principles described herein.As shown, many of the components are the same as previously discussed,however, this variant incorporates one or more plates or fin heatexchange components 1010 that is sealed to the dividing wall 228 betweenthe two chambers 112, 114 such that the circulating air or gas in thefirst chamber 112 passes over or through the part of the plates or finheat exchange components 1010 within that chamber 112 while circulatingair or gas in the second chamber 114 passes over or through the part ofthe plates or fin heat exchange components 1010 within that chamber 114so that heat (but not air) to be transferred, via the plates or fin heatexchange components 1010, between the two chambers 112, 114. Here too,depending upon the relative temperature difference, heat could be movedfrom the first chamber 112 to the second chamber 114 in someimplementations and from the second chamber 114 to the first chamber 112in other implementations.

As described above, when variants of this heat exchanger type heattransfer unit 1000 include a fan configuration where theblade-containing part of the unit 218 resides in the first chamber 112and, in accordance with the description herein, its motor 224 resides inthe second chamber 114, such that the shaft must pass through theseparating wall 228 between them, the pressure in the second chamber 114should be maintained at a higher pressure than the first chamber 112pressure (in conjunction with a sufficiently tight or other suitableseal, for example, a labyrinth seal or other tortuous path seal) tominimize or eliminate the possibility of infiltration by the hazardousair 104 into the second chamber 114.

FIGS. 11A-11B respectively illustrate, in simplified overview form,still other example variant heat transfer units 1110, 1120, in thiscase, in the form of thermosiphon-type heat exchangers that implementthe principles described herein.

Such heat transfer units 1110, 1120 do not use a compressor to circulatea cooling agent between two sets of coils that work as the evaporator1112, 1122 and condenser 1114, 1124. Rather, they rely upon conventionalprinciples wherein convection caused by changes in specific density,temperature difference, placement and gravity effect that circulation.Thus, with these type heat transfer units 1110, 1120, the coils that actas the evaporator 1112, 1122 are always physically located much lowerthan the coils that act as the condenser 1114, 1124. Thus, when thecooling agent in the evaporator 1112, 1122 undergoes a change from aliquid state to a gaseous state it rises up through piping 1116, 1126 tothe coils that act as the condenser 1114, 1124 where it returns from agaseous state to a liquid state and, via gravity, returns via otherpiping 1118, 1128 to the coils that act as the evaporator 1112, 1122.

Although not shown in FIGS. 10, 11A & 11B, it should be understood thatthe increased pressure in the chambers 114 could either be a result of apurge/pressurization system connected to that chamber 114 or,alternatively, due to higher pressure inert gas, air or nitrogenentering the chamber 114 from a cabinet to which it is attached.

Manufacturing Details

Having described the invention claimed with reference to variousrepresentative example implementation variants, some specificmanufacturing variant details will now be provided with theunderstanding that these are only provided for completeness and thatsome may be mutually exclusive relative to others in that they cannotboth be simultaneously part of the same implementation.

In this regard, some variant housings of the heat transfer units will bemanufactured from aluminum or, in some cases, plastic or a plastic (orother insulator) coated metal. With some variants, the wall(s) dividingthe two chambers will be solid welded, soldered or otherwise formed suchthat there are no seams between the two chambers through which thehazardous air might pass. Depending upon the particular implementation,the heat transfer unit can be configured such that hazardous air willenter from the bottom or one end of the unit and exit from the top orother end, or vice versa. The same will independently be the case withthe atmosphere in the volume or enclosure to be heated or cooled.

The particular configuration and number of fans that will be used canvary, as can the type of fan (e.g., axial, centrifugal, I.) used as theair movement element(s) within either or both chambers. In addition, ifair movement from the volume or enclosure is sufficient, some variantsmay not need a fan in the chamber that is isolated from the hazardousair at all.

Likewise, in some less than preferred variants, it is not inconceivablethat an explosion proof fan or some other “intrinsically safe” or“electrically safe” component could be located in the chamber throughwhich the hazardous air would pass, and such variants should beunderstood to be encompassed herein provided a substantial number, orthe most substantial potential ignition source components (in terms ofdanger or risk of causing ignition or explosion if exposed to thehazardous air) are still located in the chamber isolated from thehazardous air.

With respect to the shaft of a fan that passes through the wallseparating the two compartments, the shaft should be sealed with asuitable rotary shaft seal so as to minimize the possibility of passageof hazardous air through the seal if not eliminate it entirely.Alternatively, the fan motor and blades could be coupled with anon-physical coupling (for example, a magnetic coupling) such that therewould be no need for a shaft to pass through the wall separating the twocompartments at all.

The coil(s) in either compartment may be single stage or multi-stage asthe intended application requires, or space or design constraintsdictate.

Where the hazardous air may contain particulates, the heat transfer unitmay incorporate suitable filtration.

Finally, it is to be understood and appreciated that, in actualimplementation, heat transfer units created according to the teachingsherein will likely also include internal insulation, internal bracketsfor mounting the various components, external elements for mounting theunit to the housing to be cooled or heated and/or stabilizing the unit.For simplicity, such elements have not been shown and their lack ofinclusion should not be taken as indicating a lack of presence. Onlythose elements or components pertinent to understanding the claimedinvention have been included.

It should be understood that this description (including the figures) isonly representative of some illustrative embodiments. For theconvenience of the reader, the above description has focused on arepresentative sample of all possible embodiments, a sample that teachesthe principles of the invention. The description has not attempted toexhaustively enumerate all possible variations. In addition, asdescribed, some variations or features may be mutually exclusive in thatthey cannot be simultaneously present in a single embodiment. Thatalternate embodiments may not have been presented for a specific portionin the context of the whole, or that further undescribed alternateembodiments may be available for a portion, is not to be considered adisclaimer of those alternate embodiments. One of ordinary skill willappreciate that many of those undescribed embodiments incorporate thesame principles of the invention as claimed and others are equivalent.

What is claimed is:
 1. A method of making a heat transfer unit for usein a location where hazardous air is present, the method comprising:forming a first compartment within a housing including therein allpotential ignition source elements of the heat transfer unit, a firstheat exchange coil, and a first fan configured to cause a gas to enterthe first compartment, interact with the first heat exchange coil, andthen exit the first compartment; forming a second compartment within thehousing, sealed off from the first compartment, and including therein atleast a second heat exchange coil, and a second fan, the second fanbeing positioned within the second compartment so that, when the heattransfer unit is in operation, the second fan will cause the hazardousair to enter the second compartment, interact with the second heatexchange coil, and then exit the second compartment; the firstcompartment being configured to be pressurized such that, when the heattransfer unit is in operation, the first compartment will have a firstinternal pressure and the second compartment will have a second internalpressure, with the first internal pressure being higher than the secondinternal pressure.
 2. The method of claim 1, wherein the heat transferunit is a cooling unit and the first heat exchange coil is an evaporatorcoil.
 3. The method of claim 1, wherein the heat transfer unit is aheating unit and the first heat exchange coil is a condenser coil. 4.The method of claim 1, wherein none of the potential ignition sourceelements are designated as: explosion proof components, encapsulatedcomponents, non-incendive component, or intrinsically safe components.5. The method of claim 1, further comprising: coupling a purge andpressurization system to the first compartment.